1. Field of the Invention
The present invention relates to a local antenna for an MR device with a marker that permanently contains a substance that can be detected by MR technique.
2. Description of the Prior Art
Local antennas are employed in diagnostic MR devices for improvement of the signal-noise ratio, and thus of the image quality. The positioning of the local antennas applied to a patient in MR devices has been undertaken conventionally with the aid of a light-beam localizer which marks a region having a defined or known distance from the isocenter of the imaging region of the MR device. A center of the local antenna is first covered with the line of light generated by the light-beam localizer--e.g. by means of a corresponding positioning on a patient bed or by corresponding positioning of the patient bed with the patient. The patient is subsequently moved with the patient bed by the defined distance into the imaging region. In many MR devices the position detection is limited to a single coordinate direction, namely the coordinate axis of the path of travel of the patient bed. Also, it is impossible therein to communicate the positions of a number of simultaneously utilized local antennas to the MR device. In the simultaneous utilization of a number of local antennas it would be desirable to determine their positions and to identify the local antennas themselves. The positions could then be utilized by the MR device to select that local antenna which has the most optimal signal-noise ratio for a region of interest and which thus delivers the best resolution and imaging.
German OS 43 25 206, corresponding to U.S. Pat. No. 5,678,549, teaches a local antenna of the abovementioned type. The local antenna has a marking means that contains a substance that can be detected using MR technique. The marking means generates visible reference points in the MR image which are then utilized for localizing an anatomical abnormality. At the same time, the marking means itself can be applied as a reference point at a stereotactical auxiliary means for carrying out a biopsy of the diagnostic abnormality. The reference points visible in the MR image are necessary for precise execution, but can also be disadvantageous in other applications.
Particularly in subtraction recordings before and after the administration of a contrast agent, a marking which is imaged equally in the two source or original images would disappear due to the subtractive formation. German OS 44 42 398, corresponding to U.S. Pat. No. 5,699,800, thus describes a device with which the marking means can be selectively filled with various substances that behave differently with respect to MR imaging techniques. Visible markings thus can be generated in subtractive images. A transfusion system must be employed to exchange the substances in the marking means between the two imaging sequences. The transfusion system is relatively expensive due to the required line connections.